<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>计数器</title>
</head>
<body>
    <div id="app">
        <button @click="sub">
            -
        </button>
        <span>{{number}}</span>
        <button @click="add">
            +
        </button>
    </div>
<!-- 开发环境版本，包含了有帮助的命令行警告 -->
<script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
<script>
    var app = new Vue({
        el:"#app",
        data:{
            number:0
        },
        methods:{
            sub:function(){
                if(this.number>0){
                    this.number--
                }else{
                    alert("已经最小了")
                }   
            },
            add:function(){
                if(this.number<10){
                    this.number++
                }else{
                    alert("已经最大了")
                }  
            },
        },
    })
</script>
</body>
</html>